Improved switching circuitry for semiconductor diodes

ABSTRACT

A driver amplifier for p-i-n diodes in the phase shifters of a phased array antenna, such amplifier being arranged so as to produce, in response to a command signal from a beam steering computer, either a forward-bias or a back-bias signal for such diodes, the particular bias signal produced by such amplifier being delayed by substantially the same length of time after application of a command signal.

United States Patent 1 1 1111 3,710,145

Williamson et al. [451 Jan. 9, 1973 s41 IMPROVED SWITCHING CIRCUITRY3,259,849 7/1966 Willett et a1. ..307/317 x R EMI ND DIODES 3,290,62412/1966 Hines 07/317 x 3,295,138 12/1966 Nelson 333/31 R InventorsRobert Willinmson, Concord; 3,305,867 2/1967 Miccioli et al.......333/31 R Christos J. Georgopoulos, Lowell, 3,400,405 9/1968Patterson, Jr ..333/31 R both of Mass. Primary Examiner-Stanley D.Miller, Jr. [73] Asslgnee' 2: company Lexington Attorney-Philip J.McFarland and Joseph D. Pannone [22] Filed: Feb. 1, 1971 [57] ABSTRACT[21] Appl. No.: 111,424

A drlver amplifier for p-1-n d1odes 1n the phase sh1fters of a phasedarray antenna, such amplifier being ar- [52] US. Cl. ..307/270, 307/242,307/246, ranged so as to produce, in response to a command 307/253,307/256, 307/262, 307/319, 333/31 signal from a beam steering computer,either a for- R, 343/854 ward-bias or a back-bias signal for suchdiodes, the [51] Int. Cl. ..H03k 1/00, H03k 17/00 particular bias signalproduced by such amplifier being [58] Field of Search ,.307/208, 246,236, 256, 253 delayed by substantially the same length of time after307/260, 254, 262, 270, 317, 319, 241, 242, ppli f a comm n signal.

[56] References Cited '7 65111153 firiiiig iig iirs UNITED STATESPATENTS 3,459,969 8/1969 Jasper ..307/319 X iFifi/ERTNFLFER g F w T l I1 3 led i "8 I -r BEAM i 1 I A STEERING 1 1 1 1 I COMPUTER 45 i i 1 1 f/2 i DELAY E 1 I I Z/ 2 I I0 1 I I 1 L i J L. 1 CONTROLLER TRANSMITTERDRIVER 1 SYNC.- MULTIPLIER IRECEIVER LSYNC (NOT SHOWN) I T d 1 i 1 lim IL 1 l DRIVER AMPLIFIER- PATENTEUJM! 9 I975 SHiEI 2 OF 2 TIME F/G 2 PRIORART TINTE TIME TIME

//V VE N 70/?5 GEORGOPOULOS J ROBERT I W/LL/AMSON IMPROVED SWITCHINGCIRCUITRY FOR SEMICONDUCTOR DIODES BACKGROUND OF THE INVENTION Thisinvention pertains generally to phased array antennas for radar andparticularly to antennas of such type suing semiconductor diode phaseshifters to collimate and direct a beam of microwave energy.

It is known in the art that a matrix of so-called semiconductor diodephase shifters may be used selectively to adjust the phase of microwaveenergy passing to, or from, individual antenna elements in a phasedarray. Such diode phase shifters are operative, in accordance with aprogram determined by the parameters of the particular array and thedesired deflection angle of a beam of microwave energy, to change thelength of the electrical path of the microwave energy between eachantenna element and a source (or detector) of such energy.

When relatively large amounts of microwave energy are to be passedthrough a semiconductor diode phase shifter, it is common practice touse so-called p-i-n diodes as the switching element in such a phaseshifter. Unfortunately, however, the characteristics of p-i-n diodes andassociated elements are such that the length of time required to switchfrom a forward-bias to backbias condition is longer than the timerequired to switch in the opposite direction. It follows therefore, inview of the fact that provision must be made to prevent the propagationof microwave energy during the time in which any of the p-i-n diodes isswitching, that it is necessary to inhibit generation of microwaveenergy for a relatively long period of time whenever it is desired tochange beam direction.

Attempts have been made to reduce the time required to operate p-i-ndiodes by using driver amplifiers with output stages having specialcharacteristics. That is, it is known to provide, in the output stagesof driver amplifiers for p-i-n diodes, power transistors having lowstorage and fall times so that only the delays inherent in the switchingof p-i-n diodes are experienced. It has been found, however, that thetypes of power transistors required are extremely expensive and that,even with the best of existing power transistors, marked improvementcannot be attained.

SUMMARY OF THE INVENTION Therefore, it is a primary object of thisinvention to provide improved circuitry for operating p-i-n diodes insemiconductor phase shifters for microwave energy.

Another object of this invention is to provide improved circuitry asjust mentioned, such circuitry being adapted to operate withconventional, relatively inexpensive components.

These and other objects of this invention are attained generally in adriver amplifier for p-i-n diodes by providing, in such an amplifier,delay means operative on the control signals to a greater degree whenthe p-i-n diodes are to be driven from their back-bias to theirforward-bias conditions, the amount of delay of such control signalsbeing substantially equal to the delay inherent in such p-i-n diodeswhen being driven from their forward-bias to their back-bias conditions.

BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding ofthis invention, reference is now made to the following'description ofthe accompanying drawings, in which:

FIG. 1 is a greatly simplified sketch showing the relationship of adrive amplifier according to this invention in relation to a radarsystem; and

FIGS. 2 and 3 are sketches of the waveforms appearing at the output ofdriver amplifiers in response to command signals from a beam steeringcomputer.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, it maybe seen that the contemplated radar system includes a controller 10, abeam steering computer 12, a plurality of driver amplifiers 14, 14n, amatrix (not numbered) of phase shifters l8 l8n, and atransmitter/receiver 20. The just recited elements, except for the driveamplifiers 14 l4n, are conventional in construction and operation. Thus,the controller 10 simply produces beam steering command signals for thebeam steering computer 12 and synchronizing pulses for thetransmitter/receiver 20. It is noted, however, that, if it is desired topermit microwave energy to be propagated only after the phase shifters16 l6n have completed any required change in response to a change in thebeam steering command signal, the beam steering command signal line andthe synchronizing signal line should be interlocked in any convenientfashion. Such interlocking should inhibit the transmitter/receiver 20for a short period of time, say 1.5 microseconds, after any change inthe beam steering command signal to permit the phase shifters 16 16n tobe forward or back-biased as required. It is also noted that, forconvenience here, each phase shifter 16 l6n has been shown as a threebit phase shifter. It is not, however, essential to the inventionthat athree bit phase shifter be used.

Referring now to the exemplary driver amplifier 14, it may be seen thateach such amplifier includes a delay circuit 21, an amplifying section23, a pair of output power transistors 25, 27, a discharging transistor28 and associated elements to be described. Suffice it to say here,however, that the various elements combine in the steady state with alogic one, i.e. approximately +2 volts, on the input line from the beamsteering computer 12 so that output power transistor 25 is conductingand output power transistor 27 is cut-off. Conversely, in the steadystate with a logic zero, i.e. approximately zero volts, on the inputline from the beam steering computer 12, both output power transistors25, 27 are cut-off. On other words, in the first steady state, thecorresponding p-i-n diodes 29, 29a are ultimately connected, vialimiting resistors 31, 31a, cable 33, inductor 35, output powertransistor 25 and diode 37 to a forward-biasing current source, -E,. Inthe second steady state, the p-i-n diodes 31, 31a are connected, asindicated, through a resistor 39 (having a resistance on the order of270 kilohms), the inductor 35, cable 33 and resistors 31, 31a to aback-bias current source, +E

The delay circuit 21 is made up of a resistor 43, a capacitor 45 and atransistor 47. With the arrangement shown, it is obvious that, in thesteady state, the transistor 47 is cut-off when a logic zero is appliedto the resistor 43 from the beam steering computer 12. When the outputsignal from the latter is changed to a logic one, it is equally obviousthat the voltage on the emitter electrode (not numbered) of thetransistor 47' rises in accordance with the time constant of theintegrating circuit (resistor 43 and capacitor 45). It follows,therefore, that the threshold voltage for conduction by transistor 47 isreached only after some period of time, say 2 microseconds, has elapsedafter the change of a logic one. When transistor 47 becomes conducting,amplifier 23 produces a positive going signal which is coupled through adiode 49 and a resistor 51 to the base electrode (not numbered) of theoutput power transistor 25. It is noted that the positive going signalout of the amplifier 23 is blocked from the base electrode (notnumbered) of a discharging transistor 28 by a diode 55. The lattertransistor is biased into its cut-off condition. The positive goingsignal on the base electrode of the output power transistor 25 issufficient to cause the latter to conduct, thereby producing aforward-bias signal (via, inductor 35, cable 33 and resistors 31, 31a)to the p-i-n diodes It us noted that the current path forforward-biasing the p-i-n diodes 29, 29a initially includes a capacitor59 (which capacitor is charged to a voltage substantially equal to E,;when output power transistor 25 starts to conduct). As current is drawnfrom capacitor 59, its voltage changes approaching the forward biasvoltage, -E to permit diode 37 to conduct. Thereafter, the current pathincludes the forward bias current source, -E,. The operation ofcapacitor 59, as just described, helps discharging the cable 33 andimproves rise time of the forward-bias signal at the p-i-n diodes 29,29a.

When the output signal from the beam steering computer 12 changes from alogic one to a logic zero, the capacitor 45 may discharge, at leastpartially,

through the transistor 47 because that element is still conducting. The.time constant of the combination of the capacitor -and the emitter-basecircuit of the transistor 47, as long as the latter is conducting, isrelatively short as compared to the time constant of the combination ofresistor 43 and capacitor 45. Con-' sequently, the discharge ofcapacitor 45 occurs at a more rapid rate than its charge. Ina practicalapplication, then, transistor 47 cuts off within a few tenths of amicrosecond after a logic zero is received from the beam steeringcomputer 12. When transistor 47 ceases to conduct, amplifier 23 producesa negative going signal. Such signal is blocked by diode 49 but ispassed by diode so as to appear on the base electrode (not numbered) ofdischarging transistor 28. The emitter circuit for the latter is thencompleted, via capacitor 59, a diode and a resistor 61 so that itconducts momentarily (until capacitor 59 is charged). During this time,say a few tenthsof a microsecond, transistor 28 conducts, the storagecharge of the output power transistor 25 is removed, thereby causingthat element to cut-off more quickly than would be the case ifdischarging transistor 28 were not in the circuit. Because the currentthrough the inductor 35 cannot change instantaneously, the cut-off ofoutput power transistor 25 causes the inductor 35 to produce, for ashort period of time, a voltage spike on the base electrode (notnumbered) of the output power transistor 27, which voltage spike issufficient to turn that transistor on. A relatively high back-currentspike is, consequently, passed from back-bias source, +E,,, throughresistor 41, output power transistor 27, cable 33 and resistors 31, 31ato p-i-n diodes 29, 29a. Such a current spike is effective rapidly todeplete the storage charge of the p-i-n diodes thereby changing them totheir back-bias condition. As noted hereinbefore, when output powertransistor 27 reverts back to its cut-off condition after, say, 2microseconds, back-bias is maintained on the p-i-n diodes through thepath from the back-bias source, +E which includes resistor 39.

Having described an embodiment of a driver amplifi er according to thisinvention, reference is now made to FIGS. 2 and 3 of our driveramplifier. Thus, in FIG. 2 the upper set of curves shows that, inresponse to a negative-going signal, 81743, from a beam steeringcomputer (such signal being a command signal to switch pi-n diodes in aphase shifter from a forward-bias to a back-bias condition), some timeelapses before the voltage, V,,, reaches a desired steady stateback-bias level. With a positive-going signal, S from a beam steeringcomputer (such signal, illustrated in the lower set of curves in FIG. 2,being a command signalto switch p-i-n diodes in a phase shifter from aback-bias condition to a forward-bias condition), the requisite changein level of the voltage across the p-i-n diodes takes place almostcoincidentally with the command signal. It is apparent, therefore, thatthe generation of microwave energy in a radar system according to theprior art must be inhibited for an interval equal to the intervalbetween application of a command signal and completion of the slowerswitching direction. Typically, such as interval is in the order of 3microseconds.

Referring now to FIG. 3 it may be seen that, according to our invention,switching from a forward-bias to a back-bias condition is accomplishedin substantially the same manner (as shown in the upper set of curves inFIG. 3) as in the prior art. Application of a positivegoing signal, Sfrom a beam steering computer, i.e. a command signal to switch pi-ndiodes in a phase shifter from a back-bias to a forward-bias condition,has, however, no immediate effect on the output signal from our driveramplifier. After a period of time (which period is approximately thesame as the time taken to switch the p-i-n diodes from a forward to aback-bias condition) our circuit then operates. Obviously, therefore,the generation of microwave energy need be inhibited for an interval,typically 1.5 microseconds, as indicated by the vertical dashed lines.

It will be appreciated by those of skill in the art that reducing theperiod of time during which generation of microwave energy is inhibitedin order to change the condition of phase shifters in a phased arrayantenna is important when a large number of targets is being tracked. Itwill also be appreciated that our contemplated circuitry permits suchreduction without making it necessary to use relatively fast acting(and, therefore, expensive) semiconductor elements. It is felt, in viewof the foregoing, that this invention should not be restricted to itsdisclosed embodiment, but rather should be limited only by the spiritand scope of the appended claims.

What is claimed is:

connecting the semiconductor diodes in an associated semiconductor-diodephase shifter to a terminal;

b. second circuit means, including a second resistor, for connecting asource of back-bias voltage to the terminal;

c. third circuit means, including a first transistor, for connecting asource of forward-bias voltage to the terminal; and

. fourth circuit means, including a time delay circuit for connecting asource of binary control signals to the first transistor to switch thatelement from its conducting state to its nonconducting state inaccordance with the binary control signals, the time delay of the timedelay circuit also varying in accordance with the binary controlsignals.

2. Circuitry as in claim 1 having, additionally:

a. a second transistor, such transistor having its collector electrodeconnected through a third resistor to the source of back-bias voltage,its base electrode connected to the terminal and its emitter electrodeconnected to a junction in the first circuit means; and

. inductor means, disposed in the first circuit means between theterminal and the junction and responsive to the binary control signals,for momentarily biasing the second transistor into its conductive stateduring each period of time when the first transistor is changing fromits conducting to its nonconducting state.

3. Circuitry as in claim 2 having additionally: fifth circuit means,including a third transistor, the emitter electrode of such transistorbeing connected to the base electrode of the first transistor, thecollector electrode of such transistor being connected to a dischargingload and the base electrode of such transistor being in circuit with thefourth circuit means and the discharging load, the third transistorthereby being biased into its conducting state only during each periodof time when the first transistor is changing from its conducting to itsnonconducting state.

1. In a phased array antenna assembly for microwave energy, suchassembly incorporating a matrix of antenna elements, each one of suchelements having associated therewith a semiconductor-diode phase shifterto change, in accordance with binary control signals, the phase ofmicrowave energy to and from each one of such elements, separatecircuitry for selectively forward-biasing and back-biasing thesemiconductor diodes in each semiconductordiode phase shifter, each suchseparate circuitry including: a. first circuit means, including a firstresistor, for connecting the semiconductor diodes in an associatedsemiconductor-diode phase shifter to a terminal; b. second circuitmeans, including a second resistor, for connecting a source of back-biasvoltage to the terminal; c. third circuit means, including a firsttransistor, for connecting a source of forward-bias voltage to theterminal; and d. fourth circuit means, including a time delay circuitfor connecting a source of binary control signals to the firsttransistor to switch that element from its conducting state to itsnonconducting state in accordAnce with the binary control signals, thetime delay of the time delay circuit also varying in accordance with thebinary control signals.
 2. Circuitry as in claim 1 having, additionally:a. a second transistor, such transistor having its collector electrodeconnected through a third resistor to the source of back-bias voltage,its base electrode connected to the terminal and its emitter electrodeconnected to a junction in the first circuit means; and b. inductormeans, disposed in the first circuit means between the terminal and thejunction and responsive to the binary control signals, for momentarilybiasing the second transistor into its conductive state during eachperiod of time when the first transistor is changing from its conductingto its nonconducting state.
 3. Circuitry as in claim 2 havingadditionally: fifth circuit means, including a third transistor, theemitter electrode of such transistor being connected to the baseelectrode of the first transistor, the collector electrode of suchtransistor being connected to a discharging load and the base electrodeof such transistor being in circuit with the fourth circuit means andthe discharging load, the third transistor thereby being biased into itsconducting state only during each period of time when the firsttransistor is changing from its conducting to its nonconducting state.